EVAPORATION AT HIGH ELEVATIONS IN HAWAII

An experiment was conducted to measure evaporation at high elevations on a tropical island mountain and to compare these measurements with estimates from Penman, Penman-Van Bavel, Penman-Monteith, and Priestley-Taylor models. Hourly evaporation and other microclimatological data were measured at three sites on Haleakala, Maui, Hawaii. Evaporation during the observation period increased with elevation, averaging 3.3 mm day-1 at 950 m, 3.6 mm day-1 at 1650 m, and 6.4 mm day-1 at 2130 m. The spatial pattern of evaporation on Haleakala is dominantly a function of elevation relative to the position of the inversion. The residual of measured minus modeled evaporation, as well as the ratio of evaporation to net radiation increased with elevation. The rate of night-time evaporation, also increasing with elevation, suggests a source of non-radiative energy. Results indicate that air above and within the inversion layer in the- Hawaiian Islands region provides a source of heat advection that substantially increases potential evaporation at high elevations.